Hydroalcoholic hand sanitizing gels have found increasing use by consumers and in institutional facilities such as schools, hospitals, and restaurants. Their advantages include the ability to instantly kill germs and bacteria on the hands. Soap and water are not required. The hydroalcoholic gels can be formulated to provide conditioning and moisturizing benefits, as well as a pleasant after-feel on the hands.
High alcohol sanitizing gels are known in the art. They typically contain from about 60 to about 70 percent alcohol. They may also contain emollients, moisturizers, conditioners, fragrances, dyes, and colorants. Thickening agents are used to obtain a gelled composition. The thickening agents employed must be capable of thickening the high alcohol content gel compositions without leaving a residue on the skin that is overly sticky. Prior art thickening agents include addition polymers of acrylic acid crosslinked with an unsaturated polyfunctional agent such as a polyallyl ether of sucrose. These carboxy vinyl polymers are described in U.S. Pat. Nos. 2,798,053 and 3,133,865, and have the CTFA (Cosmetic, Toiletry and Fragrance Association) adopted name of “carbomer.” Carbomers are the preferred thickening agents because they are cost-effective and aesthetically pleasing. Carbomers have the ability to thicken compositions comprising over 90 percent ethanol and/or isopropyl alcohol. They also have the ability to produce clear systems with shear thinning rheology for effective dispensing and application to the hands.
The key to formulating hydroalcoholic gels with carbomers is choosing the correct neutralizing agent. The neutralizing agent neutralizes at least a portion of the carboxyl groups within the carbomer molecules, converting the acidic carbomer to a water soluble salt, and facilitating optimum thickening. The prior art, however, teaches that sodium hydroxide, and other well known neutralizers do not work in high alcohol hydroalcoholic systems, due to the low level of available water, and the low solubility of the carbomer salt. Table 1 summarizes the neutralizing agents for various alcohol levels recommended in. TDS-237, entitled “Neutralizing Carbopol™ and Pemulen™ Polymers in Aqueous and Hydroalcoholic Systems,” from B.F. Goodrich (1998). As shown in Table 1, sodium hydroxide and potassium hydroxide are only recommended for hydroalcoholic systems comprising up to about 20% and about 30%, respectively, alcohol. Likewise, U.S. Pat. No. 4,956,170 to Lee teaches that sodium hydroxide, triethanolamine, monoethanolamine, and dimethyl stearylamine are not compatible as neutralizing agents because they do not adequately form a gel of desirable viscosity in a 60% ethanol composition. In fact, many neutralizing agents, including all of the GRAS neutralizing agents listed in 21 CFR 184, and all of the amino acids listed in 21 CFR 172.320 are known not to provide the desired viscosity in a 60% or greater alcohol composition as presently produced.
TABLE 1Neutralizing agents for HydroalcoholicSystems Recommended in Prior ArtMaximum % AlcoholNeutralizing agent20Sodium Hydroxide30Potassium Hydroxide60Triethanolamine60Tris Amino80Amino Methyl Propanol (AMP-95 ®)90Neutrol TE90Diisopropanolamine90Triisopropanolamine>90Ethomeen C-25
An antimicrobial skin sanitizing composition comprising a high concentration of alcohol, a thickening agent and a neutralizing agent that is designated by the FDA as Generally Recognized As Safe (GRAS) under 21 CFR 184 or that is permitted for consumption as an amino acid under 21 CFR 172.320, would be desirable.